Composer's lightest note in rising melody (10)
I believe the answer is:
palestrina
'composer's' is the definition.
(Giovanni Pierluigi da Palestrina)
'lightest note in rising melody' is the wordplay.
'lightest' becomes 'palest' ('pale' can be similar in meaning to 'light').
'note' becomes 'n' (abbreviation**).
'in' indicates putting letters inside.
'rising' is a reversal indicator (going up in a down clue).
'melody' becomes 'air' ('air' can be a synonym of 'melody').
'air' reversed gives 'ria'.
'n' inserted into 'ria' is 'rina'.
'palest'+'rina'='PALESTRINA'
(Other definitions for palestrina that I've seen before include "Italian Renaissance composer" , "He composed music" , "musician" , "16th century Italian choral composer" .)